1. Field of the Invention
The present invention relates to a vehicle air conditioner including an air-outlet mode selecting device for opening and closing air outlet openings. The air-outlet mode selecting device includes two rotary doors each of which has an outer peripheral door surface turning with a rotary shaft.
2. Related Art
An air-outlet mode selecting mechanism for opening and closing air outlet openings in an air conditioner for a vehicle is broadly divided into the following three types of air-outlet mode selecting devices. The first type of air-outlet mode selecting device, as shown in FIG. 22, opens and closes a defroster opening 20, a face opening 21 and a foot opening 22 by the use of a face/defroster selector door 110 made of a cantilever plate door and a foot door 100 made of a cantilever plate door. Here, the plate-shaped foot door 100 is provided with a rotary shaft 100a at one end thereof and is turned around the rotary shaft 100a. Similarly, the plate-shaped face/defroster selector door 110 is provided with a rotary shaft 110a at one end thereof and is turned around the rotary shaft 110a. 
The second type of air-outlet mode selecting device, as shown in FIG. 23, opens and closes the defroster opening 20, the face opening 21 and the foot opening 22 by the use of a foot door 100, a face door 110 and a defroster door 120 each of which is made of a butterfly door. Here, the butterfly door 100 is provided with a rotary shaft 100a at the center thereof and is turned around the rotary shaft 100a. Similarly, the butterfly door 110 is provided with a rotary shaft 110a at the center thereof and is turned around the rotary shaft 110a, and the butterfly door 120 is provided with a rotary shaft 120a at the center thereof and is turned around the rotary shaft 120a. 
The third type of air-outlet mode selecting device opens and closes the face opening 21, the defroster opening 20 and the foot opening 22 by the use of a single rotary door having an outer peripheral door surface turning with a rotary shaft. Further, the outer peripheral door surface turning with the rotary shaft is arranged at a position separated by a predetermined distance outward in the radial direction from the center of the rotary shaft. This outer peripheral door surface is usually shaped like an arc having its center at the rotary shaft.
In the first type of air-outlet mode selecting device, the defroster/face selector door 110 and the foot door 100 are respectively constructed of the cantilever plate doors, so the doors 100, 110 need to be operated against the pressure of blowing air applied to the whole surface of the plate door. Further, there are cases where the doors 100, 110 need to be operated against their self-weights. As described above, because the doors 100, 110 need to be operated against the pressure of blowing air and the self-weight, the first type of air-outlet mode selecting device presents a problem that a door operating force becomes large.
In the second type of air-outlet mode selecting device, the three doors 100 to 120 are constructed of the butterfly doors. The butterfly door has the rotary shaft at the center of the door plate, so the force applied to one side of the door plate by the air pressure and the self-weight is opposite to the force applied to the other side of the door plate by the air pressure and the self-weight. Therefore, the second type of air-outlet mode selecting device has an advantage of canceling effects of the air pressure and the self-weight, thereby reducing the door operating force as compared with the first type of air-outlet mode selecting device. However, when the butterfly door is used, the door plate is located near the center of the air passage of the respective openings when the respective openings are fully opened (see door 110 in FIG. 23). Due to this construction, an air flow resistance increases, air blowing volume is reduced, and air blowing noises (whizzing noises) increase when the respective openings are fully opened. Then, in a case where the butterfly door is located directly behind an air mixing portion in which cold air and hot air are mixed with each other, there is a phenomenon in which the cold air and the hot air from the air mixing portion flow separately on the front surface side and the rear surface side of the door plate of the butterfly door. This presents a problem of increasing variations in the temperature of air to be blown into a passenger compartment.
According to the third type of air-outlet mode selecting device, the face opening 21, the defroster opening 20 and the foot opening 22 can be opened and closed by the single rotary door, so the third type of air-outlet mode selecting device has an advantage of reducing the number of doors and simplify a link mechanism for operating the doors as compared with the first and second types of air-outlet mode selecting devices. However, the third type of air-outlet mode selecting device, for the following reasons, deteriorates the mounting performance in a vehicle. That is, in the third type of air-outlet mode selecting device, all of the face opening, the defroster opening and the foot opening need to be arranged in an arc shape along the turning path of the outer peripheral door surface of the rotary door. On the other hand, the air conditioning unit is arranged in a place that is inside the instrument panel (i.e., dashboard) of the vehicle and is subjected to extreme spatial constraint. Thus, it is difficult to perform the arrangement of three air outlet openings of the face opening, the defroster opening and the foot opening in the shape of an arc.
Further, in order to ensure the respective air volumes blown off from the three air outlet openings, the areas of the respective air outlet openings need to be enlarged and hence the area of the outer peripheral door surface of the rotary door needs to be enlarged. As a result, the rotary door is increased in size, and the mounting performance of the air conditioning unit in the vehicle is further deteriorated.